A color picture tube includes a panel, a funnel made of glass, and a neck portion. Red, green and blue phosphor dots are applied to the inner surface of the panel to form a fluorescent surface, and a shadow mask assembly is disposed at a predetermined space with the phosphor dots. A studpin is buried and mounted on a predetermined location of the inner surface of the panel in order to install the shadow mask assembly.
In the color picture tube, electron beams are emanated from respective electron guns, and impinge upon corresponding phosphor dots on the fluorescent surface through an aperture of the shadow mask assembly. The fluorescent surface luminates by the electron beams and this light becomes pixels that form an image.
Since the image of the color picture tube is watched through an outer surface of the panel, the thickness and curvature of the inner surface of the panel have a great influence on the quality of the image. Besides, since the studpin determines a relationship of the placement of the shadow mask assembly as to electron beams, a high quality image may not be produced if the shadow mask is not in its predetermined location. For such reasons, it is desired that the standard of the color picture tube panel be closely examined during the processes of inspection.
During the inspection process the standard of the panel is examined by measuring the thickness of an edge portion of the panel and a thickness of a center portion or the panel is typically measured. A linear variable differential transformer (LVDT) is typically used for measuring the standard of a color picture tube panel. The LVDT is a well known device that displays an electrical signal of inductance when it is placed into contact with the thing being measured. The electrical signal displayed by the LVDT varies depending on the distance between the LVDT and the thing being measured. Accordingly, an operator can arrange a number of LVTDs to measure the thickness of the panel at different locations as well as the curvature of the inner surface of the panel.
However, the use of LVTDs to accurately measure the standard of a color picture tube panel requires that the panel be tested a minimum of three times, each time requiring the involvement of an operator to insure the setup of the panel and the LVTDs. Accordingly, the use of LVTDs to measure the standard of a panel is a manpower intensive operation having a high inspection time per panel.
It is, therefore, desirable that a panel-testing apparatus for a color picture tube be constructed that is capable of successively and automatically measuring data of the thickness of the edges and a center portion of the panel, the curvature of an inner surface of the panel, and the position of a studpin in a manner that simplifies the testing processes, reduces testing time per panel, improves operator productivity, and reduces manpower.